1. Field of the Invention
The present invention relates to a paper transportation device for transporting an original document to an image scanning unit in a scanner, a facsimile, a copying machine or the like.
2. Description of the Related Art
A scanner, a facsimile, a copying machine or the like includes a paper transportation device such as an Automatic Document Feeder (ADF) that feeds a plurality of original documents sequentially. The plurality of original documents stacked on a document tray can be transported continuously and automatically to a scanning position by the paper transportation device.
FIG. 9 is a schematic perspective view showing an appearance of a copy-and-facsimile multifunction peripheral 900 having an ADF. As shown in the drawing, the copy-and-facsimile multifunction peripheral 900 includes a scanning table 901, a document pressing plate 902, an operation panel 903, a main frame 904 and paper feed cassettes 905. On the scanning table 901, a platen glass where an original document is to be placed is provided. The original pressing plate 902 presses and fixes the original document on the platen glass. The operation panel 903 is used for inputting a start of a scanning process of the original document or the like. The main frame 904 includes an image recording unit which records an image onto recording paper and a transmission unit which transmits the image electrically through a public network or the like. The paper feed cassettes 905 accommodate recording papers for recording the scanned image.
In the copy-and-facsimile multifunction peripheral 900, the ADF in the document pressing plate 902 constitutes the paper transportation device. By the ADF, the sheeted original document placed on a document tray 906 is transported downwards to a paper discharge tray 907, which is provided below the document tray 906, while front and back sides of the original document are reversed (so as to make a U-turn). While being transported, when the original document passes a scanning position on the platen glass, an image of the original document is scanned by an image scanning unit such as a Charge Coupled Device (CCD) provided inside the scanning table 901.
In the conventional paper transportation device, a transportation path leading from the document tray 906 via the scanning position to the paper discharge tray 907 is formed of an outer guide surface and an inner guide surface having a shape of the letter U sideways. For example, the outer guide surface is formed of a housing of the document pressing plate 902. The inner guide surface is formed of a paper guide disposed inside the document pressing plate 902.
Metal plates are secured on both sides of the paper guide by screws. Bearings are mounted in holes formed on the metal plates, and a transportation roller shaft on which a transportation roller made of silicon rubber is secured is provided appropriately. Accordingly, the transportation roller is disposed at a prescribed position in the transportation path, and the original document is transported through the transportation path by rotation of each transportation roller.
Furthermore, in the document pressing plate 902, a metal gear stud is secured to the metal plate between two metal brackets by a caulk. A drive transmitting gear is supported axially by the gear stud. In addition, a drive unit, which includes a motor for applying a drive force to the drive transmitting gear, is provided in the document pressing plate 902. The drive force is transmitted from the motor of the drive unit to the transportation roller shaft. According to the above-described conventional paper transportation device, although rigidity is high, there is an increase in weight. In addition, a number of components that constitute the paper guide and the drive unit or the like becomes large, and an assembling process is complicated. Therefore, the paper transportation device results being expensive, and a maintenance work is troublesome.
Thus, there is proposed a paper transportation device in which a paper guide, which is a guide surface of a transportation path having a shape of the letter U sideways, is formed integrally by a frame made of resin such as plastics. Accordingly, a number of components of the paper guide or the like and a number of assembling steps can be reduced, and the cost of the paper transportation device can be reduced.
However, since paper is transported while being slid against the guide surface of the paper guide, static electricity is generated by friction of the paper and the paper guide, and the static electricity is accumulated on the paper. As a result, there are cases in which the transported paper is skewed by being adhered to the paper guide or the like or a transportation speed becomes unstable, and an image quality of a scanned image is deteriorated. If the paper guide is made of resin, such a generation of the static electricity becomes even more apparent.
Recently, the scanner, the facsimile and the copying machine or the like are demanded to be even more downsized and economical. In addition, the paper transportation device to be equipped in these machines are also demanded to be even more downsized and economical. Therefore, a reduction in the number of components and a simplification of the assembling process are required even more.
Moreover, in the scanner, the facsimile and the copying machine or the like, recycling of resources or the like is becoming important. Each of the components of the paper transportation device is required to be disassembled according to different kinds of materials such as metals and plastics, and then to be reused or disposed. Therefore, not only the assembling process but also the disassembling process carried out when disposing the components is preferable to be simplified.